N-halohydantoin compounds are used commercially in industrial and recreational water treatment to provide biocidal action and to control bacterial growth. Recently, these compounds have also been used in household automatic toilet bowl cleaners. Examples of N-halohydantoins currently being used in these applications include N,N'-dichloro- and N,N'-dibromo- derivatives, as well as mixtures of N,N'-chloro and -bromo derivatives.
N-halohydantoin compounds are typically produced as solid particulates. They are often compacted by mechanical pressure into forms such as briquettes, tablets and pucks. These "compacts" are normally subjected to various stresses and shocks during packaging, transport and end-use. Because of this, it is highly desirable to have a composition for compaction that not only molds easily, but better withstands stresses and shocks.
Various binders have been used in the compaction process. Most organic materials, however, cannot be used as binders with N-halohydantoins because of the N-halohydantoins' strong oxidizing properties. Severe reactivity with the N-halohydantoins results in substantial discoloration of the finished product.
U.S. Pat. No. 3,412,021 teaches using polymers as binders, with copious amounts of water, to form 1-bromo-3-chloro-5,5-dimethylhydantoin into sticks or rods. A paste is made that consists of at least 25% water. However, excess water renders the polymers inactive, thereby preventing curing. The resulting compacts are not acceptable. In addition, compacts formed by this process are not as hard as is desirable, unless a post-application drying process is performed. The cost of evaporating water to make an acceptable product is prohibitive.
U.S. Pat. No. 4,677,130 describes adding dry, particulate alkali metal or alkaline earth metal salts to N-halohydantoins, and then compacting. While this process does not require water (as in U.S. Pat. No. 3,412,021 ), use of alkali earth metal salts has several drawbacks. For example, while the compact formed, e.g., using magnesium stearate, is thermally stable, it has a lower decomposition temperature (as measured by differential scanning calorimetry). This is caused by the reaction between the N-halohydantoin and the alkali earth metal salt. Off-color products result where ambient temperature is not sufficiently controlled. Nor is it possible to modify the rate of dissolution of the N-halohydantoin using alkali salts. Modifying the rate of dissolution is desirable, for example, to extend the functional lives of toilet bowl cleaners and urinal tablets.
Canadian patent 1,230,825 describes the use of borax (e.g. Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O) as a binder for N-halogenated hydantoins. Adding borax produces tablets that are essentially dust-free, have a high minimum break strength, and have dissolution characteristics that can be modified by varying the amount of borax. However, the patent indicates that a separate additive, such as stearic acid or sodium stearate, is required to lubricate die surfaces. Such additives melt at low temperature (e.g. 55.degree.-65.degree. C.), resulting in a markedly lower decomposition temperature for the compacted products.